WPS: Clear sent_carrier to avoid errors in python script

This is needed to avoid errors when reporting the result of an NFC
connection handover that failed.

Signed-hostap: Jouni Malinen <jouni@qca.qualcomm.com>

hostapd/wps-ap-nfc.py

@@ -120,6 +120,7 @@ def wps_handover_resp(peer):
     print "Trying to handle WPS handover"
 
     srv = HandoverServer()
+    srv.sent_carrier = None
 
     nfc.llcp.activate(peer);